The Argent Crusade was the evolution of the Argent Dawn, a group of people from the Alliance and Horde that joined together to serve the Light. The Argent Crusade focused on fighting off the armies of the Scourge and putting an end to Arthas. Only Tirion Fordring and the adventurers that killed Arthas knew that Bolvar Fordragon was the new Lich King.
Tirion and the Argent Crusade later participated in the assault of the Broken Shore in the Burning Legion's third invasion of Azeroth. However, Tirion and many crusaders fell during the battle. The Order of the Silver Hand was reformed, and the Argent Crusade disbanded.